Reflective planar lightwave circuit waveguide

ABSTRACT

A method of making a planar lightwave circuit (PLC) waveguide capable of being integrated with a surface-mounted component is presented. The method entails etching a silicon substrate to form a slanted wall, forming a nonreflective waveguide portion on the silicon substrate, and depositing a reflective layer on the slanted wall. Light travels through the nonreflective waveguide portion in substantially a first direction, and the light from the nonreflective waveguide portion strikes the reflective layer to be redirected in a second direction. The second direction may be the direction toward the surface-mounted component. A PLC waveguide device made with the above method is also presented.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional application of U.S. patent applicationSer. No. 12/199,655 filed on Aug. 27, 2008, U.S. Pat. No. 7,933,478which claims the benefit of U.S. Provisional Patent Application No.61/067,150 filed on Feb. 25, 2008, the contents of which areincorporated by reference herein.

BACKGROUND

1. Field of Technology

The invention relates generally to optical waveguides and particularlyto optical coupling of a silica-based waveguide and a surface-mountdevice.

2. Related Art

Optical waveguide devices formed on planar substrates have becomeimportant elements for various optical network applications such asmultiplexers and demultiplexers in dense wavelength divisionmultiplexing (DWDM) systems and components in passive optical networks(PON). In the field of optical communications, use of monolithicsilica-based planar lightwave circuits (PLCs) with optical passivedevices is well known. FIG. 1 is a cross-sectional view of an opticalwaveguide device 1 formed on a planar substrate 10. On the planarsubstrate 10, there are a lower cladding layer 12, a core layer 14, andan upper cladding layer 16. These layers may be made of pure or dopedsilicon dioxide (SiO₂). Light travels through the core layer 14.

With new developments in optical communication technologies, there is anincrea sing need for integration of optical, optoelectronic (e.g., laserdiodes and photodiodes), and electronic components using low-costpassive alignment techniques to develop high functionalityoptoelectronics modules such as TOSA and ROSA. It is desirable tocombine the low-cost silica PLC platform with an active device such as alaser diode or a photodiode to make a high-functionality optoelectronicmodule. This integration is difficult, however, because laser diodes andphotodiodes are frequently made with III-V semiconductor substrateswhile PLCs are usually made with silicon substrates. While it ispossible to make the PLC devices with III-V materials, this would makethe integrated system expensive because III-V materials are moreexpensive than silicon.

The challenge in integrating the silica-based PLC with III-V-basedactive device lies in the interface. This challenge sometimes stems fromthe active device being a surface-mount device. Photodiodes, forexample, are often surface-mount devices. To provide an effectiveinterface, a method has been proposed whereby a micromirror using asilica-based PLC is used for optical path conversion. In this proposal,the micromirror is made of a resin by utilizing wettability control andsurface tension effect. A well is first etched in the PLC and then thesurface of a different area of the well is treated to make the contactangle of the resin on the surface different. The resin is put in thewell by surface tension effect to form a mirror in the well. The mirrorangle is controlled by the contact angles.

A problem with the above approach is that aside from the mirror groove,two termination grooves and a long resin supply groove are used to formthe mirror. This increases the size of the mirror area. Also, the resinsupply groove extends to the edge of the chip, making a deep groovealong the chip. This deep groove along the chip may pose a problem formaking electrode contact with the surface-mounted active device. Thislong groove may also affect the layout of the PLC waveguide.

A second approach is to fabricate an integrated mirror in a silica-basedPLC. In this approach, a superficial layer is created by treating thesurface in an oxygen plasma. During this treatment, the waveguidesurface made of silica is subjected to intense ion bombardment by oxygenions with an average energy of about 300 eV. Following this treatment, alayer of amorphous silicon is deposited as a hard mask. Then, chemicaletching is carried out in a buffered (15%) hydrofluoric acid solution.Since the superficial layer etching rate is higher than the isotropicetching rate, a slope is formed in/on the waveguide. After depositingthe aluminum as reflecting layer, a mirror is formed.

A problem with the second approach is that the mirror is formed bydifferent etching rates in the surface-treated layer and the normallayer in isotropic etching. Because the surface-treated layer is usuallyshallow due to the limitations with ion bombardment, the mirror isusually short and covers a small part of the waveguide core layer. Thesmall mirror size means only part of the waveguide mode is reflected,limiting the reflecting efficiency.

SUMMARY

In one aspect, the invention is a method of making a planar lightwavecircuit (PLC) waveguide capable of being integrated with asurface-mounted component. The method entails etching a siliconsubstrate to form a slanted wall, forming a nonreflective waveguideportion on the silicon substrate, and depositing a reflective layer onthe slanted wall. Light travels through the nonreflective waveguideportion in substantially a first direction, and the light from thenonreflective waveguide portion strikes the reflective layer to beredirected in a second direction. The second direction may be thedirection toward the surface-mounted component.

In another aspect, the invention is a planar lightwave circuit (PLC)waveguide capable of being integrated with a surface-mounted component.The PLC waveguide includes a silicon substrate having a sidewall formedin an inner area away from edges of the silicon substrate, anonreflective waveguide portion formed on the silicon substrate, and areflective layer formed on the slanted wall. Light travels through thenonreflective waveguide portion in substantially a first direction.Light from the nonreflective waveguide portion strikes the reflectivelayer to be redirected in substantially a second direction, the seconddirection being substantially perpendicular to the first direction.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an optical waveguide device formedon a planar substrate.

FIG. 2A is a cross-sectional view of an embodiment of the PLC waveguideof the invention.

FIG. 2B is a perspective view of the embodiment of the PLC waveguideshown in FIG. 2A.

FIGS. 3-15 are views of different embodiments of the PLC waveguide ofthe invention.

FIG. 16A a top view diagram depicting the position of the nonreflectivewaveguide portion in the PLC waveguide of the invention.

FIGS. 16B and 16C are perspective views of an embodiment of the PLCwaveguide of the invention.

FIGS. 17 and 18 are top view diagrams depicting a tapered shape of thenonreflective waveguide portion in the PLC waveguide of the invention.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings which illustrate several embodiments of the present invention.It is understood that other embodiments may be utilized and mechanical,compositional, structural, electrical, and operational changes may bemade without departing from the spirit and scope of the presentdisclosure. The following detailed description is not to be taken in alimiting sense, and the scope of the embodiments of the presentinvention is defined only by the claims of the issued patent.

It will be understood that when an element or layer is referred to asbeing “on” another element or layer, it can be directly on the otherelement or layer or intervening elements or layers may be present. Incontrast, when an element is referred to as being “directly on” anotherelement or layer, there are no intervening elements or layers present.

This invention includes a low-cost monolithic integrated mirror madewith a silica-base PLC technology that is capable of interfacing asurface-mounted component, even a surface-mounted III-V component. Themonolithic integration is cost efficient, highly reliable, and suitablefor large-scale production. For planar active devices such assurface-emitting laser diodes and photodiodes, the key component is amonolithic integrated mirror that can reflect light traveling in ahorizontal direction (i.e., parallel to the board) to redirect it in avertical direction (i.e., orthogonal to the board). This way, the lightcan be coupled to an active device mounted on a surface.

FIG. 2A is a cross-sectional view of a reflective PLC waveguide 30having a slanted wall 32. As shown, the PLC waveguide 30 has a siliconsubstrate 34 that is partially etched to form a slanted wall 32. Informing the slanted wall 32, a lower portion LP and an upper portion UPare formed on the silicon substrate 34, with the slanted wall 32positioned between the lower portion LP and the upper portion UP. Thereflective layer 36 forms an angle of about 20° to 70° with respect tothe horizontal surface 35 of the substrate 34. The slanted wall 32 formsan angle of about 20° to about 70° with respect to a horizontal surface35 of the substrate 34; for example, the slanted wall 32 may form anangle of about 54.7° with respect to the horizontal surface 35 of thesubstrate 34. In some embodiments (e.g., the embodiments shown in FIGS.2A, 3, 10A, and 10B), the reflective layer 36 has a substantiallysimilar angle as the slanted wall 32 with respect to the horizontalsurface 35. The PLC waveguide 30 is monolithic.

After the slanted wall 32 is formed, a nonreflective waveguide portion40 is formed. Light 70 travels through the nonreflective waveguideportion 40 substantially in a first direction (a horizontal directionwith respect to the figure), propagates across a gap 48 between thenonreflective waveguide portion 40 and the slanted wall 32, and reachesa reflective layer 36 that is coated on the slanted wall 32. The gap 48may be filled with air, although this is not a limitation of theinvention. The reflective layer 36 redirects the light 70 substantiallyin a second direction (a vertical direction with respect to the figure).In this particular embodiment, the reflective layer 36 is formeddirectly on the silicon substrate 34. The height of the slanted wall 32is selected to make the far field mode of the nonreflective waveguideportion 40 locate at the linear area of the reflective layer 36.

The nonreflective waveguide portion 40 includes a bottom cladding layer42, a core layer 44, and a top cladding layer 46. To form thenonreflective waveguide portion 40, the bottom cladding layer 42 isformed (e.g., deposited, thermally grown) on the surface of the siliconsubstrate 34 using a suitable method, preferably in a substantiallyconstant thickness. The core layer 44 is then formed, followed by thetop cladding layer 46, both in a substantially constant thickness. Thecladding layers 42, 46 and the core layer 44 may all be made of SiO₂.Then, the part of the formed layers that cover the slanted wall 32 andits adjacent areas are removed, for example by etching (e.g., with SF₆),to expose the substrate surface. The reflective layer 36 is then formed.The shape and size of the reflective layer 36 may be adapted to theapplication as long as the light 70 strikes a flat surface of thereflective layer 36.

The nonreflective waveguide portion 40 has an exit facet 41 thatinterfaces the gap 48. In FIG. 2A, the exit facet 41 forms approximatelya 90° angle with respect to the horizontal surface of the substrate 34.However, this is not a limitation of the invention, as will be explainedbelow.

FIG. 2B is a perspective view of the PLC waveguide 30 of FIG. 2A. Thecore layer of the nonreflective waveguide portion 40 is shown by brokenlines. To substantially keep the light traveling through the core layer,the core layer and the surrounding cladding layers have different dopingconcentrations. For example, the core layer may have a higher index ofrefraction than the surrounding cladding layer. As shown, the slantedwall 32 is a sidewall that is formed in the inner part of the chip, awayfrom the edges of the chip. As shown in FIG. 2B, the slanted wall 32 iswider than the nonreflective waveguide portion 40 in plan view. Forexample, the width of the slanted wall may be about 100 μm or more, andthe width of the nonreflective waveguide portion 40 may be about 1 μm ormore. When viewed from the side, the thickness of the nonreflectivewaveguide portion 40 may be about 30˜50 μm, while the slanted wall maybe higher than 30 μm. Although these are typical dimensions forsilica-on-silicon PLC, dimensions may be smaller for other silicon-basedPLCs.

FIG. 3 is a cross-sectional view of a second embodiment of the PLCwaveguide 30. This embodiment is similar to the embodiment of FIG. 2,with a primary difference being that the exit facet 41 forms an angle γwith respect to the horizontal surface 35. Although the angle γ is lessthan 90° in this particular example, this is not a limitation of theinvention. The angle γ of the exit facet 41 may be changed to controlthe direction in which light 70 travels after it exits the nonreflectivewaveguide portion 40, and is useful for controlling the point ofincidence on the reflective layer 36.

The angle γ of the exit facet 41 may be created by etching. A person ofordinary skill in the art will understand how to adjust processvariables such as plasma power and etchant composition to achieve thedesired angle γ.

FIG. 4 is a cross-sectional view of a third embodiment of the PLCwaveguide 30. This embodiment is similar to the embodiment of FIG. 2,with a primary difference being the existence of a thin bottom claddinglayer 42 on the slanted wall 32. As shown, the reflective layer 36 isformed on the bottom cladding layer 42.

To make this embodiment, the substrate 34 is partially etched to formthe slanted wall 32, the lower portion LP, and the upper portion UP. Thebottom cladding layer 42, the core layer 44, and the upper claddinglayer 46 are conformally formed on the substrate 34. The layers are thenpartially etched. In the particular example that is depicted, some ofthe bottom cladding layer 42 is left unetched on the lower portion LPand the upper portion UP. Due to this partial removal, the bottomcladding layer 42 is thinner on slanted wall 32 and the area of theupper portion UP that is adjacent to the slanted wall 32 than on theother parts of the substrate 34. The height of the slanted wall 32 maybe controlled to make the waveguide far field mode locate at the desiredarea of the reflective layer 36. The depth to which the cladding layersare etched is at least partly determined by how to make the waveguidefar field mode locate at the linear area of the reflective layer.

Unlike the embodiments shown in FIGS. 2A, 3, 10A, and 10B, thereflective layer 36 and the slanted wall 32 may have different angles inthe embodiment of FIG. 4. This may also be the case in the embodimentsshown in FIGS. 4-9 and 11, 12A, 12B, 12C, 13A, 13B, 14A, and 15 below.

FIG. 5 is a cross-sectional view of a fourth embodiment of the PLCwaveguide 30. This embodiment is substantially similar to the embodimentof FIG. 2, with a primary difference being that a cladding layer 50 isformed on the slanted wall 32. The cladding layer 50, which may be madeof SiO₂, is formed on the slanted portion of the slanted wall 32 andalso on the upper portion UP. The cladding layer 50 may be formed at thesame time as the top cladding layer 46 and/or the bottom cladding layer42. The reflective layer 36 is formed on the cladding layer 50. Thereflective layer 36 is at about the same height level as thenonreflective waveguide portion 40.

The embodiment of FIG. 5 may be made by forming the bottom claddinglayer 42 and the core layer 44, etching the layers from the upperportion UP, the slanted wall 32, and the part of the lower portion LPthat is adjacent to the slanted wall 32. Then, the top cladding layer 46is formed and partially etched to form the deepest part of the gap 48.The reflective layer 36 is then formed on top of the top cladding layer46 (which is shown as the cladding layer 50). The top cladding layer 46in the reflective portion of the PLC waveguide 30 may be etchedpartially to make the far field mode of the nonreflective waveguideportion 40 locate at the linear part of the mirror.

Alternatively, after forming the bottom cladding layer 42 and the corelayer 44, the top cladding layer 46 may be formed to prepare thenonreflective waveguide portion 40. Then, the top cladding layer 46 andthe core layer 44 are etched completely or partially to make the farfield mode of the nonreflective waveguide portion 40 locate at thelinear part of the mirror.

FIG. 6 is a cross-sectional view of a fifth embodiment of the PLCwaveguide 30. This embodiment is similar to the embodiment of FIG. 5,with a primary difference being the existence of an α-Si layer 52. Afterforming the core layer 44, it is desirable for the top surface of thecore layer 44 to be at approximately the same level as the top surfaceof the slanted wall 32 so that there would be no gap between the contactmask and the waveguide surface during lithography. In the embodiment ofFIG. 5, the light 70 might strike the reflective layer 36 close to or atthe rounded areas instead of at the linear area. By forming the α-Silayer 52 conformally after forming the core layer 44, then forming thetop cladding layer 46 and partially/completely (completely, in the caseof FIG. 6) etching the top cladding layer 46, the linearity of theeffective reflective surface can be increased. As shown, the α-Si layer52 is formed directly on the silicon substrate 34, between the siliconsubstrate 34 and the cladding layer 50. The thickness of the α-Si layer52 is controlled to ensure that the reflective coating 36 covers all thefar field mode of the PLC waveguide 30. The α-Si layer 52 may besubstituted with a SiN layer.

To form the embodiment of FIG. 6, a temporary layer (not shown) isformed on the substrate 34 and selectively removed from thenonreflective waveguide portion 40. On the slanted wall 32 and the upperportion UP, the temporary layer may be a SiN layer. Where the bottomcladding layer 42 is formed, the temporary layer may be a photoresistlayer or an SiN layer. If the bottom cladding layer 42 is thermallygrown, then a locos process may be used. Then, the α-Si layer 52 isformed and patterened on the slanted wall. The core layer 44 is formed,and selectively removed along with the bottom cladding layer 42 from thedesired areas. The top cladding layer 46 is formed, part of which formsthe cladding layer 50. The cladding layer 50 is then selectively removedto form the deepest portion of the gap 48. The reflective layer 36 isformed and selectively removed.

FIG. 7 is a cross-sectional view of a fourth embodiment of the PLCwaveguide 30. This embodiment is similar to the embodiment of FIG. 6,with a primary difference being the position of the reflective layer 36.Unlike in the embodiment of FIG. 6, the reflective layer 36 ispositioned directly on the α-Si layer 52, between the α-Si layer 52 andthe cladding layer 50.

The embodiment of FIG. 7 is made using a process that is similar to theprocess for FIG. 6. However, to change the location of the reflectivelayer 36, the reflective layer 36 is formed after the formation of theα-Si layer 52 and before the formation of the cladding layer 50.

FIG. 8 is a cross-sectional view of a seventh embodiment of the PLCwaveguide 30. In this embodiment, which has no gap 48, the reflectivelayer 36 is formed between the bottom cladding layer 42 and the corelayer 44 on the slanted wall 32. The light 70 travels through the corelayer 44 in the lower portion LP, then strikes the lower part of thereflective layer 36 to get reflected upward, as shown.

To make this seventh embodiment, the substrate 34 is etched to form theslanted wall of a desired angle, the bottom cladding layer 42 is formed,and a reflective layer is formed on the bottom cladding layer 42. Thereflective layer is removed everywhere except for an area including theslanted wall 32, and the core layer 44 is formed. Then, the top claddinglayer 46 is formed on the core layer 44. Each layer is formed to have asubstantially constant thickness. Here, the top cladding layer 46provides protection to the reflective layer 36.

FIG. 9 is a cross-sectional view of an eighth embodiment of the PLCwaveguide 30. This embodiment is similar to the embodiment of FIG. 8,with a primary difference being that the slanted wall 32 is shorter.When the slanted wall 32 is short enough, the top surface of the topcladding layer 46 becomes substantially flat. To flatten the topsurface, the top cladding layer 46 covering the reflective layer 36 maybe etched partially or completely. This embodiment is made using thesame process as the embodiment of FIG. 8.

FIG. 10A is a cross-sectional view of a ninth embodiment of the PLCwaveguide 30. In this embodiment, the slanted wall 32 is an inner wallof a well 33. Although the well 33 is shown as a V-groove in the figure,this is not a limitation of the invention (e.g., the well could beshaped like a U). The well 33 is preferably formed by etching (e.g., wetetching) the silicon substrate 34, and at least a part of the inner wallof the well 33 makes about a 54.7-degree angle with respect to ahorizontal surface, such as the surface of the upper portion UP.

To make this embodiment, the well 33 is formed in the silicon substrate34, and the lower portion LP of the silicon substrate 34 is etched toform a sloped portion 60. Any suitable silicon process, such as graytone mask, may be used to form the sloped portion 60. Usually, after thetop cladding layer 46 is formed, the top and bottom corners of thereflective layer 36 will be rounded (as shown below in FIG. 12B). As aresult, the light 70 does not always strike the reflective layer 36 onits linear area, making light difficult to control. Forming the slopedportion 60 lowers the nonreflective waveguide portion 40 relative to theslanted wall 32 to move the light 70 to a linear area on the reflectivelayer 36. The bottom cladding layer 42 is formed on the sloped portion60 of the substrate 34 as well as on the upper portion UP. The bottomcladding layer 42, the core layer 44, and the top cladding layer 46 areformed substantially conformally, then etched from the well 33. Then,the reflective layer 36 is formed on the slanted wall 32 by depositionand etching. The reflective layer 36 is formed on the part of theslanted wall 32 that receives the light exiting from the core layer 44of the sloped portion 60. The depth by which the nonreflective waveguideportion 40 is etched is controlled to make the waveguide far field modelocate at the linear area of the reflective layer 36. In determining thelength of the sloped portion 60, any excess signal loss due to the slopeis taken into account.

FIG. 10B is a cross-sectional view of a tenth embodiment of the PLCwaveguide 30. This embodiment is similar to the embodiment of FIG. 10A,with a primary difference being the angle of the exit facet 41. In theembodiment of FIG. 10A, the nonreflective waveguide portion 40 has anexit facet 41 that forms a right angle with respect to the surface 35 ofthe silicon substrate 34. In the embodiment of FIG. 10B, the exit facet41 forms an angle γ that is greater than 90° with respect to ahorizontal surface. Method of forming the angle is described above, inreference to FIG. 3. The angle of the exit facet 41 may be changed tocontrol the direction in which light 70 travels after it exits thenonreflective waveguide portion 40, and is useful for controlling thepoint of incidence on the reflective layer 36.

FIG. 11 is a cross-sectional view of a eleventh embodiment of the PLCwaveguide 30. This embodiment is similar to the embodiment of FIG. 10A,with a primary difference being an incomplete etching of the bottomcladding layer 42 and possibly also the core layer 44. As shown, some ofthe bottom cladding layer 42 and the core layer 44 remain in the well33, and some of the bottom cladding layer 42 remains on the slanted wall32 and part of the upper portion UP that is adjacent to the well 33. Inthis structure, enough of the layers formed in the well 33 are removedto create an unobstructed path for light to travel from the slopedportion 70 of the waveguide to the reflective layer 36. The process formaking this embodiment is similar to the process that was describedabove for FIG. 4, with the addition of forming the well 33 and thesloped portion 60.

In the embodiment of FIG. 10A, the angle of the reflective layer 36 isdetermined by the angle of the slanted wall 32, which has goodlinearity. In the embodiment of FIG. 11, the reflecting layer 36 is onthe partially etched bottom cladding layer 42. Due to the regrowth ofsilica, the corners of the reflective layer 36 may be rounded. In thiscase, etch depth is selected to ensure that light will strike thereflective layer 36 on a linear portion.

FIG. 12A is a cross-sectional view of a twelfth embodiment of the PLCwaveguide 30. This embodiment is similar to the embodiment of FIG. 11,with a primary difference being that the reflective layer 36 is formedbetween the core layer 44 and the bottom cladding layer 42. Thereflective layer 36 being “buried” under the top cladding layer 46 andthe core layer 44, it is protected from various environmental elements.The light 70 that exits the tapered portion of the waveguide will travelacross the gap 48 and travel through the top cladding layer 46 and thecore layer 44 before striking the reflective layer 36 to get reflectedin the second (vertical) direction. The process for making thisembodiment is similar to the process described above for FIG. 11, exceptthat the reflective layer 36 is formed before the core layer 44 isformed.

FIG. 12B is a cross-sectional view of a thirteenth embodiment of the PLCwaveguide 30. This embodiment is similar to the embodiment of FIG. 12A,with a primary difference being that the reflective layer 36 is on thetop cladding layer 46. The process for making this embodiment is similarto the process described above for FIG. 12A, except that the reflectivelayer 36 is formed after the top cladding layer 46.

FIG. 12C is a cross-sectional view of a fourteenth embodiment of the PLCwaveguide 30. This embodiment is similar to the embodiment of FIG. 12B,with a primary difference being that there is no top cladding layer 46under the reflective layer 36. The top cladding layer 46 has beenselectively removed from parts of the PLC waveguide 30 other than thenonreflective waveguide portion 40.

FIG. 13A is a fifteenth embodiment of the PLC waveguide 30. Thisembodiment is similar to the embodiment of FIG. 12A, with a primarydifference being that the nonreflective waveguide portion 40 is slantedsuch that the exit facet 41 forms an angle θ with respect to a planethat slices the nonreflective waveguide portion 40 at a right angle.With respect to FIG. 13A, the plane would extend into the page and beorthogonal to the lengthwise direction of the nonreflective waveguideportion 40. In addition, the nonreflective waveguide portion 40 itselfmay be tilted, for example by being formed on the sloped portion 60,such that the lengthwise direction of the nonreflective waveguideportion 40 forms a tilt angle β with respect to an axis that is normalto an edge of the reflective layer 36. Specifically, the embodimentshown in FIGS. 13A and 13B show that the exit facet 41 can be slantedvertically (e.g., downward) to reduce the return loss at the exit facet41. The formula for determining the tilt angle β is provided below, inreference to the embodiment of FIG. 16A.

FIG. 14A is a cross-sectional view of a sixteenth embodiment of the PLCwaveguide 30. This embodiment is similar to the embodiment of FIG. 12B,with a primary difference being the formation of the α-Si layer 52. Theα-Si layer 52 is formed between the bottom cladding layer 42 and thecore layer 44. The thickness of the α-Si layer 52 is controlled toensure that it covers all the far field mode of the PLC waveguide 30locate at the linear area of the reflective layer 36. FIG. 14B is aperspective view of the embodiment shown in FIG. 14A. As shown, theslanted wall 32 is formed in the inner part of the PLC waveguide 30. Inthe embodiment of FIG. 14B, the slanted wall 32 extends across the widthof the PLC waveguide 30.

FIG. 15 is a cross-sectional view of a seventeenth embodiment of the PLCwaveguide 30. This embodiment is similar to the embodiment of FIG. 14Awith a primary difference being the position of the α-Si layer 52. Here,the α-Si layer 52 is formed between the core layer 44 and the topcladding layer 46.

FIG. 16A is a top view diagram depicting the position of thenonreflective waveguide portion 40 in an embodiment of the invention.FIGS. 16B and 16C are perspective views of the PLC waveguide 30depicting the position of the nonreflective waveguide portion 40. FIGS.16A, 16B, and 16C show that the exit facet 41 can be slantedhorizontally (so that one side of the exit facet 41 is closer to thereflective layer 36 than the other) as well as vertically to reduce thereturn loss at the exit facet 41. The exit facet 41 is slanted such thatit forms an angle θ with respect to a plane that slices thenonreflective waveguide portion 40 at a right angle, orthogonally to thelengthwise direction of the nonreflective waveguide portion 40. Inaddition, the nonreflective waveguide portion 40 may be tilted such thatthe lengthwise direction of the nonreflective waveguide portion 40 formsa tilt angle β with respect to an axis that is normal to an edge of thereflective surface 36. The angles θ and β are used to adjust the angleof incidence at the reflective layer 36. For the light 70 to reach thereflective layer 36 at a substantially normal angle, the tilt angle iscalculated as follows:β=a sin(n _(eff) sin(θ))−θwherein the horizontal tilt angle β indicates the tilt of thenonreflective waveguide portion 40, n_(eff) is the effective index ofrefraction for the nonreflective waveguide portion 40, and θ indicatesthe severity by the exit facet 41 is slanted with respect to the rest ofthe nonreflective waveguide portion 40.

Although the gap 48 is filled with air in the above examples, this isnot a limitation of the invention and the gap may be filled with anysubstance that allows light to travel through it and is different fromthe material that makes up the nonreflective waveguide portion 40. Ifthe gap 48 were to be filled with a material having an index ofrefraction n_(gap), the formula for determining the angle β would beadjusted as follows:β=a sin [(n _(eff) /n _(gap))sin(θ)]−θ.

FIG. 17 is a top view diagram depicting the shape of the nonreflectivewaveguide portion 40 in an embodiment of the invention. In theembodiments described above, the width W of the waveguide portion 40remained substantially constant except where the exit facet 41 slanted.In this embodiment, the nonreflective waveguide portion 40 has a taperedshape when viewed from the top, such that the width decreases asdistance to the exit facet 41 decreases. This tapering technique may beused to control the waveguide mode size exiting the exit facet 41, whichcontrols the far field of this mode, and the location and/or directionof the light beam exiting the exit facet 41. In an exemplary embodiment,the width of the straight waveguide is about 3 to about 8 μm and thenarrowest portion of the tapered section may be as narrow as 1 μm. This,however, is not a limitation of the invention. Likewise, the taper shapeis not limited to the particular one that is shown in the drawings, andmay be linear, parabolic, exponential, etc.

FIG. 18 is a top view diagram depicting the shape of the nonreflectivewaveguide portion 40 in another embodiment of the invention. Thisembodiment is similar to the embodiment of FIG. 17 except that the widthof the nonreflective waveguide portion 41 increases as distance to theexit facet 41 decreases. The widest section of the tapered part of thenonreflective waveguide portion 40 may be as wide as about 12 μm.Between the embodiments of FIG. 17 and FIG. 18, the untapered part ofthe nonreflective waveguide portion 40 may be about 3-8 μm, and thetapered part may be about 1-12 μm, depending on the silica waveguidecore design. These dimensions are not limitations of the invention but adescription of an exemplary embodiment. Dimensions of the device mayvary a lot depending on the waveguide index difference. Further,although FIG. 17 and FIG. 18 each shows a horizontally slanted exitfacet 41, the tapered design of the nonreflective waveguide portion 40is not limited to being used with a slanted exit facet 41. Furthermore,the tapered design of the nonreflective waveguide portion 40 may be usedwith a PLC waveguide design of FIG. 8 or 9.

The device and method described herein have advantages over some of theexisting devices and methods for integration of silica-based PLC andIII-V-based active device. One of the existing methods of achieving thisintegration entails forming a mirror in a groove by using wettabilitycontrol and surface tension effect. However, as mentioned above, the enddevice made with this method has termination grooves and a long resinsupply groove extending to the edge of the chip. In contrast, the deviceof the invention has just a localized groove, resulting in a simplifieddesign.

Another existing method for integration of silica-based PLC andIII-V-based active device entails creating a superficial layer bybombarding a silica surface with oxygen ions. With this method, the enddevice has a mirror fabricated in the waveguide core layer. This meansthe mirror covers only a small part of the waveguide, reflecting onlypart of the waveguide mode. The device of the invention allows greaterflexibility by making it possible to form the reflective layer on thebottom cladding layer or the top cladding layer as well as the corelayer. Since the reflective layer can be formed on more than one ofthese layers, the mirror size can be increased as well to improve thereflection efficiency. Further, in the embodiments that have a gapbetween the waveguide (the non-reflective waveguide) and the reflectivelayer, the exit facet on the waveguide can be adjusted to achieve aneven higher reflection efficiency.

Another limitation of this second existing integration method is that itis only usable with silica waveguides. The general sequence for thissecond existing method is as follows: 1) deposit the waveguide bottomcladding layer and/or the core layer, 2) selectively ion-bomb certainparts of the deposited layer, 3) etch the deposited waveguide layers toform a slant, then 4) deposit the reflective layer and the top claddinglayer. The substrate itself is not etched with this existing method. Inthe method of the invention, the slanted wall is formed by etching thesilicon substrate, not just the waveguide layer(s). Hence, the etchingof the silicon substrate is generally performed before the conformaldeposition of the waveguide layers and the reflective layer. Hence,unlike the existing method, the method of the invention can be used withany waveguide material other than silica as long as the waveguidematerial can be conformally deposited or otherwise formed to a fairlyuniform thickness.

Embodiments of the invention are described herein with reference tocross-section illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures) of the invention. Assuch, variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, embodiments of the invention should not be construed aslimited to the particular shapes of regions illustrated herein but areto include deviations in shapes that result, for example, frommanufacturing. The regions illustrated in the figures are schematic innature and their shapes are not intended to illustrate the actual shapeof a region of a device and are not intended to limit the scope of theinvention.

While the invention has been described in terms of particularembodiments and illustrative figures, those of ordinary skill in the artwill recognize that the invention is not limited to the embodiments orfigures described. In many of the embodiments described above, thevarious features can be mixed differently. For example, the position ofthe reflective layer 36 in FIGS. 14 and 15 may be changed so that thereflective layer 36 is “buried” as in FIG. 12A. A person of ordinaryskill in the art will appreciate, too, that most of the layers shownhere may be deposited or thermally grown.

Although the invention is herein described with a focus on integratingPLC with photodiode devices, the invention may be adapted forintegrating PLC and surface-emitting devices, such as laser (forPLC-VCSEL integration). Furthermore, while the invention is hereindescribed in the context of silica-on-silicon-based PLC, the structureand method disclosed herein may be applied to other silicon-based PLCswhere the waveguide bottom cladding, core, and top cladding can beformed on the substrate conformally.

Therefore, it should be understood that the invention can be practicedwith modification and alteration within the spirit and scope of theappended claims. The description is not intended to be exhaustive or tolimit the invention to the precise form disclosed. It should beunderstood that the invention can be practiced with modification andalteration and that the invention be limited only by the claims and theequivalents thereof.

What is claimed is:
 1. A method of making a planar lightwave circuit(PLC) waveguide capable of being integrated with a surface-mountedcomponent, the method comprising: etching a silicon substrate to form aslanted wall; forming a nonreflective waveguide portion on the siliconsubstrate, wherein light travels through the nonreflective waveguideportion in substantially a first direction; depositing a reflectivelayer on the slanted wall so that the light from the nonreflectivewaveguide portion strikes the reflective layer to be redirected in asecond direction; wherein the nonreflective waveguide portion has anexit face that is spaced apart from the slanted wall by a gap, andwherein the light coming out of the exit facet travels across the gap ina first direction before striking the reflective layer, the gap beingfilled with a material having a different index of refraction from thenonreflective waveguide portion.
 2. The method of claim 1, wherein thereflective layer forms an angle of between about 20° and about 70° withrespect to a surface of the silicon substrate, and wherein the seconddirection is substantially perpendicular to the first direction.
 3. Themethod of claim 1, wherein forming the slanted wall comprises wetetching the silicon substrate.
 4. The method of claim 1, wherein formingthe nonreflective waveguide portion comprises: forming a bottom claddinglayer; removing a part of the bottom cladding layer; forming a corelayer; removing a part of the core layer; forming a top cladding layer;and removing a part of the top cladding layer.
 5. The method of claim 4,wherein the forming of the bottom cladding layer, the core layer, andthe top cladding layer is completed prior to the removing of one or moreof the bottom cladding layer, the core layer, and the top claddinglayer.
 6. The method of claim 4, wherein the removing of the core layerand the top cladding layer comprises completely removing the core layerand the top cladding layer from the slanted wall while removing of thebottom cladding layer comprises leaving a layer of bottom cladding layeron the slanted wall.
 7. The method of claim 4, wherein the reflectivelayer is formed directly on either the bottom cladding layer or the topcladding layer.
 8. The method of claim 7 further comprising forming thereflective layer after forming the top cladding layer, such that thecladding layer is the top cladding layer and the reflective layer isformed directly on the top cladding layer.
 9. The method of claim 7,wherein the cladding layer is the bottom cladding layer, furthercomprising forming the reflective layer directly on the bottom claddinglayer.
 10. The method of claim 7 further comprising forming thereflective layer between the top cladding layer and the bottom claddinglayer.
 11. The method of claim 4, wherein the reflective layer is formedon top of the core layer.
 12. The method of claim 4 further comprisingforming the reflective layer under either the bottom cladding layer orthe top cladding layer.
 13. The method of claim 4, wherein the bottomcladding layer, the core layer, and the top cladding layer arecompletely removed from the slanted wall before the forming ofreflective layer, such that the reflective layer is formed directly onthe slanted wall.
 14. The method of claim 4 further comprising: forminga temporary layer on the slanted wall before forming the bottom claddinglayer and the core layer; and removing the temporary layer beforeforming the top cladding layer.
 15. The method of claim 14 furthercomprising forming an α-Si layer on the slanted wall after forming thetemporary layer.
 16. The method of claim 14 further comprising forming aSiN layer on the slanted wall after forming the temporary layer.
 17. Themethod of claim 1 further comprising forming an α-Si layer on thesilicon substrate.
 18. The method of claim 15, wherein the α-Si layer isformed directly on the slanted wall.
 19. The method of claim 17, whereinthe α-Si layer is formed directly on the bottom cladding layer.
 20. Themethod of claim 17, wherein the α-Si layer is formed directly on thecore layer.
 21. The method of claim 17, wherein the reflective layer isformed directly on the α-Si layer.
 22. The method of claim 1 furthercomprising forming a SiN layer on the silicon substrate.
 23. The methodof claim 22, wherein the SiN layer is formed directly on the slantedwall.
 24. The method of claim 22, wherein the SiN layer is formeddirectly on the bottom cladding layer.
 25. The method of claim 22,wherein the SiN layer is formed directly on the core layer.
 26. Themethod of claim 22, wherein the reflective layer is formed directly onthe SiN layer.
 27. The method of claim 1, wherein forming thenonreflective waveguide portion comprises: forming a bottom claddinglayer; forming a core layer; and forming a top cladding layer, whereinthe thickness of each of the bottom cladding layer, the core layer, andthe top cladding layer is substantially constant.
 28. The method ofclaim 1, wherein forming the nonreflective waveguide portion comprises:forming a bottom cladding layer; forming a core layer; and forming a topcladding layer such that the portion of the top cladding layer that ison the slanted wall is substantially flat.
 29. The method of claim 1further comprising adjusting an angle of the exit facet to control theangle of incidence at the reflective layer.
 30. The method of claim 29,wherein adjusting the angle comprises slanting the exit facet such thatthe exit facet forms a slant angle θ with respect to a plane that isorthogonal to a lengthwise direction of the nonreflective waveguideportion.
 31. The method of claim 30, wherein the nonreflective waveguideportion is tilted such that a lengthwise direction of the nonreflectivewaveguide portion forms a tilt angle β with respect to an axis that isorthogonal to an edge of the reflective layer, wherein β=a sin(n_(eff)sin(θ))−θ, n_(eff) being the effective index of the nonreflectivewaveguide portion.
 32. The method of claim 30 further comprising fillingthe gap with a material having an index n_(gap).
 33. The method of claim32, wherein the adjusting comprises tilting the nonreflective waveguideportion such that a lengthwise direction of the nonreflective waveguideportion forms a tilt angle β with respect to an axis that is orthogonalto an edge of the reflective layer, wherein β=a sin[(n_(eff)/n_(gap))sin(θ)]−θ, n_(eff) being the effective index of thenonreflective waveguide portion.
 34. The method of claim 1 furthercomprising adjusting the relative positions of the exit facet and thereflective layer such that the light coming out of the exit facetstrikes a flat portion of the reflecting surface at a substantiallynormal angle.
 35. The method of claim 1 further comprising tapering thenonreflective waveguide portion such that its width decreases asdistance to the exit facet decreases.
 36. The method of claim 1 furthercomprising tapering the nonreflective waveguide portion such that itswidth increases as distance to the exit facet decreases.
 37. The methodof claim 1 further comprising varying a width of the nonreflectivewaveguide portion such that a first end of the nonreflective waveguideportion has a different width than a second end of the nonreflectivewaveguide portion.
 38. The method of claim 1, wherein forming theslanted wall comprises forming a well in the silicon substrate, theslanted wall being a sidewall of the well.
 39. The method of claim 38,wherein one side of the well is higher than the other and the reflectivelayer is formed on the higher slanted wall.
 40. The method of claim 38,wherein the well is a V-groove.
 41. The method of claim 38, wherein thewell is a U shape groove.
 42. The method of claim 38, wherein formingthe nonreflective waveguide portion comprises: forming a bottom claddinglayer; removing a part of the bottom cladding layer; forming a corelayer; removing a part of the core layer; forming a top cladding layer;and removing a part of the top cladding layer.
 43. The method of claim42 further comprising completely removing the bottom cladding layer, thecore layer, and the top cladding layer from the well.
 44. The method ofclaim 42 further comprising: forming the bottom cladding layer, the corelayer, and the top cladding layer on the silicon substrate and in thewell; and removing a portion of the formed layers from an area in thewell to create an exit facet of the nonreflective waveguide portion anda gap between the exit facet and the slanted wall.
 45. The method ofclaim 1 further comprising forming a sloped portion on a part of thesilicon substrate on which the nonreflective waveguide portion isformed.
 46. The method of claim 45 wherein the sloped portion is on apart of the silicon substrate across the well from the slanted wall. 47.The method of claim 45, wherein one side of the well is higher than theother and the reflective layer is formed on the higher slanted wall. 48.The method of claim 45 further comprising forming the bottom claddinglayer, core layer and the top cladding layer in the well to form thenonreflective waveguide.
 49. The method of claim 45, wherein the slopedportion becomes closer to the substrate as it extends toward the slantedwall.